The present disclosure relates to a print head having a plurality of nozzles, each nozzle independently capable of ejecting ink onto a substrate. In particular, the disclosure relates to a valve assembly for such a print head.
Drop-on-demand inkjet printers typically include a print head having an array of nozzles. During printing, ink is ejected through particular nozzles based on the nature of a character to be printed on a suitable medium. Ink is not ejected through every nozzle at all times during a printing process. Rather, only select nozzles are utilized at any one time depending on the nature of the character to be printed. Generally, drop-on-demand inkjet printers differ from continuous inkjet printers, in which a constant stream of drops are passed between charged electrodes, because ink is not ejected through all of the orifices during a particular printing process.
Drop-on-demand printers may be used to print information onto products moving along a packaging line. Typically the printer is stationary and it is necessary to ensure that the printer is controlled so as to print correctly onto the moving products. Drop-on-demand printers generally comprise a linear array of nozzles, each connected to an ink supply by a valve. By the operation of the valves, ink is projected from the nozzles to be used in printing. Typically, seven or 16 nozzles may be provided over a vertical distance of, for example, 2.7 inches. The vertical resolution provided by the array of valves is therefore relatively low.
The main cause of low resolution in valve jet printers is the physically large size of the solenoid used in the valves. To overcome this issue, it is known that the solenoids can be coupled to the nozzles by flexible tubes, so that the spacing of the nozzles can be smaller than the spacing of the valves. However, this is problematic in that the tubes may become clogged, especially when using quick drying ink. Various solutions to this problem have been used such as the design shown in U.S. Pat. No. 5,602,575, which couples a remote solenoid to the valve and nozzle by a wire. However, this solution requires a moving ink seal for the wire to pass through, and also each wire may need occasional adjustment, such as after shipping. Another potential solution is miniaturizing the solenoid, but this causes greater heating effect and adds cost.